These machines have a substantially cylindrical outer casing defined by body which is hermetically sealed by a cover by means of rivets from which protrude the connection terminals through which the machine itself is powered.
A rotary electric machine comprises a stator, rigidly connected to the body, and a rotor, rotatably connected thereto.
Rotary electric machines of particular relevance include brushless motors and direct current motors.
A brushless motor has a wound stator and a permanent magnet rotor, whereas a direct current motor has a permanent magnet stator and a wound rotor, called armature.
A power supply circuit for the motor is housed in the casing and is powered through the above mentioned connection terminals.
The aforementioned motors are used especially in the automotive field for driving centrifugal ventilators, double or single, or axial.
The armature or the wound stator comprises a core and a plurality of windings around two or more pole pieces of the core. The windings are insulated from the pole pieces by interposed plastic insulators.
Generally speaking, a fan of plastic material, set in rotation by the rotor, may be provided inside the casing to produce a cooling air flow inside the electric machine.
The Applicant, who has developed numerous solutions for heavy-duty, sealed electric machines—for example, see documents WO2009019563 and WO2009019562 —has identified an unexpected problem hitherto unknown in the trade.
More specifically, during a test on centrifugal ventilators running at 100° C. for 4 hours, the outer casings opened and the cover and body came apart.
Also, during a similar test on nine single-shaft motors, five casings opened, with covers and casing bodies coming apart.